With a gas turbine engine, a number of different components rotate relative to fixed components under extremely tight tolerances. For example, the compressor and turbine sections of a gas turbine engine include radially outwardly extending blades, which collectively form a rotor. Such rotors rotate relative to a fixed engine case which forms a stator, with a very small annular gap between the rotor and stator. To increase the efficiency and operation of the gas turbine engine, it is important that such gaps be maintained so as to allow for proper rotation, but do so at as small a dimension as necessary to limit air leakage through the gap.
In order to minimize leakage through such gaps, seals are employed in gas turbine engines. Such seals can be contacting seals such as labyrinth or brush seals, or non-contacting seals such as hydrostatic seals. While labyrinth seals can be effective they require that all parts be manufactured and maintain at extremely tight tolerances, and can generate significant amounts of heat at the knife edge and seal rub interface. Brush seals can also be effectively, but can be prone to coking and are largely uni-directional in their sealing capability. Hydrostatic seals, on the other hand, employ a plurality of circumferentially spaced shoes extending from spring elements mounted to the stator. Such spring biased movement afforded to the shoes enables the gap between the rotor and stator to be properly maintained at all times as the velocity of the air flowing through the gap increases and decreases.
While hydrostatic seals are effective, as gas turbine engine are subjected to extreme temperature ranges from start-up through maximum speed, particularly in the hot sections of the engine such as the turbine and diffuser, significant vibrations in the seal can be encountered. Such vibrations may be particularly harsh during engine cold starts, wherein the seals can become damaged by such vibrations, in some cases to the extent that overall sealing effectiveness may be compromised.
It can therefore be seen that apparatus for damping such vibrations in hydrostatic seals of gas turbine engines are needed.